This application claims the priority of 198 39 951.0-21, filed Sep. 2, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a steering system for non-track-bound motor vehicles, with a steering handle, e.g. steering wheel, actuated by the driver, a steering actuating drive for steering displacement of steerable vehicle wheels, a desired steering-angle transmitter which can be actuated by the steering handle, and an actual steering-angle transmitter which can be actuated by the steerable vehicle wheels. A regulating arrangement controls the steering actuating drive as a function of a comparison between the desired values and actual values of the steering angle and continuously checks itself and sensors interacting with it for malfunctions. A mechanical or hydraulic positive coupling is arranged between the steering handle and the steerable vehicle wheels and, when the regulating arrangement is operating correctly, is opened or remains open (inactive normal state) and, if the regulating arrangement is defective, is automatically closed (active special state).
Known steering systems which operate on the "steer-by-wire" concept are fundamentally familiar and are being developed for future motor vehicles. These systems offer the fundamental advantage that, at least as regards the regulating arrangement and the associated sensors, they are suitable for a very wide variety of vehicles without design modifications. On one hand, virtually any transmission ratio between the actuating displacement of the steering handle and the change in the steering angle of the steered vehicle wheels can be achieved by appropriate programming. There is moreover the possibility of connecting the regulating arrangement to additional sensors in order to automatically allow for or eliminate parameters to be specified, e.g. the effects of side winds.
In order to be able to guarantee the required degree of safety in the event of system faults, provision is made to automatically activate an operating mode for abnormal operation or emergency operation if a fault occurs in the regulating arrangement or signals that are to be evaluated by the regulating arrangement fail. In this operating mode, a positive coupling is provided between the steering handle and the steered vehicle wheels. The steering system thus operates in principle in the manner of a conventional steering system, although the mechanical steering column customary in conventional steering systems can be replaced, if required, by other mechanical systems or by hydraulic systems, in particular hydrostatic systems.